A person with average length upper arms seated in a properly designed straight back chair having armrests will have elbows well supported. However, a person with short upper arms or one seated in an improperly designed chair may experience a strained posture. Improperly supported elbows or elbows that dangle because of no support whatsoever, such as with armless secretarial-type chairs and the like, will experience overloading of the upper trapezius muscles. Sustained antigravity stresses (also called "gravity stresses") imposed on the trapezius muscles may refer pain upward along the posterolateral aspect of the neck to the mastoid process, and are a major source of what is known as "tension nechache." See, J. Travell & D. Simons, Myofascial Pain and Dysfunction: The Trigger Point Manual, Williams & Wilkins, at 184-85 and 196-97. The latter reference recognizes that antigravity stresses on the upper trapezius in normally proportioned individuals can be avoided by using chairs with armrests of the correct height to provide proper elbow support. Disturbances caused by antigravity stresses are especially troublesome for persons such as secretaries, typists, stenographers, draftsmen, medical technicians, and the like whose seating arrangements provide little, if any, elbow support. The usual chair used by such persons (hereafter "secretarial chair") has a generally horizontally disposed seat whose underside is centrally supported on an upwardly directed pillar base. The lower end of the base is typically accommodated with a plurality of radially outwardly directed, spoke-like legs which carry swivel-mounted casters at their ends. A generally vertically disposed backrest is supported on one or more columns extending vertically, generally centrally up at the back of the seat. The pillar base may be telescoping or provided with other means to permit selective height adjustment of the seat above the floor. In many cases, the backrest column support is likewise constructed to permit independent height adjustment of the backrest relative to the seat. The majority of secretarial chairs are, however, armless so that they present no obstruction when drawn closely into a table. Those which do have arms, have arms that are either fixed or else not conveniently adjustable relative to other parts of the chair to permit proper positioning to support arms when drawn in to a table or desk for performing raised hand mechanical operations, such as typing.
Aronowitz U.S. Pat. No. 4,466,665 shows a secretarial chair for office use which has integrally molded arm and lower back sections adapted to provide lumbar support to a person sitting in the chair. The height of the arm/backrest combination is adjustable relative to the seat by selective positioning vertically along a strap column. No provision is made for adjustment of the arm section relative to the backrest section, nor to vary the lateral spacing of one armrest relative to the other.
British Patent Specification No. 1,481,185 shows a chair having left and right armrests carried on vertically extending upper ends of left and right bent rod carrier posts whose lower ends extend laterally inward to connect rigidly to opposite points on the underside of the seat. A downward opening, vertical recess within each armrest acts with the carrier post to provide a lockable telescopic connection by which the armrest can be slidably height adjusted relative to the seat, independently of positioning of the backrest. The same connection permits pivoting of the armrest to establish a desired angular orientation of the vertical plane of the armrest about the axis of the rod upper end. There is, however, no provision made for adjustment of the lateral spacing of one armrest rod attachment point relative to the other, and the rests are full length rests that, if kept in an arm supporting position, would interfere with bringing the seat under a desk or table.
French Patent Publication No. 2,558,360 discloses armrests mounted at the forwardly directed ends of a generally horizontal, crescent-shaped bracket on a secretarial-type chair for independent slidable height adjustment on the same column which carries a lumbar supporting backrest. The underside of the armrests are provided with transverse slots that enable selective adjustment of the lateral spacing of the arms relative to one another, but only within the limitations of the width dimensions of the armrests. No provision is made for relative adjustment of the height of one armrest relative to the other.
Aaras et al. U.S. Pat. No. 4,277,102 discloses a chair for employees doing routine factory jobs that has armrests mounted on support posts and the posts mounted to the seat body by means of universal joints. Despite the great freedom of movement, though, positional adjustment of the armrests in such an arrangement is made awkward because of the arcuate nature of the pivotal movements which hinders making horizontal adjustment while vertical adjustment is maintained, and vice versa. Moreover, the support posts do not provide armrest support without obstructing the ability to draw the chair up to a desk for typing, etc.